On older versions of Android, before 5 I think, you could go to wifi settings and view the saved password.
On the latest versions this option is not there. There is a file on your phone named wpa_supplicant.conf . You have to have root access to get to it. The file is /data/misc/wifi/wpa_supplicant.conf
If you are on a later version of Android and do not have root access, you pretty much cannot obtain the information you are asking for.